Engineering and Construction

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In the design-bid-build method, the general contractor is selected through competition. The owner obtains multiple bids for the project from which the general contractor, who provides the “best value for money,” is selected. Within this overall approach, several  versions are available to suit the requirements of the project and the particular needs of  the owner. Collectively, these delivery versions are referred to as the   design bid-build  (DBB) method because in this version, the design, bid, and construction phases of a  project are sequential, and one phase does not begin until the previous phase has been  completed,  Figure 1.7 . Following are three commonly used versions of the DBB method  of delivery:

  •    DBB method—competitive sealed bidding (open bidding)
  •    DBB method—competitive sealed proposal
  •    DBB  method— invitational  bidding   (closed  bidding)  

FIGURE 1.7  Sequence of operations in the design-bid-build (DBB) method of project delivery. Note that the owner’s approval is required before proceeding from one phase or stage to the next.

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Selecting the general contractor is a crucial part of a project. A number of selection methods exist. The method used in selecting the general contractor, its timing, and the contractor’s obligations under the contract distinguishes one project delivery method from the other. Some of the most commonly used delivery methods are:

•    Design-bid-build  method
•    Design-negotiate-build  method
•    Construction manager as agent method
•     Construction  manager  at  risk   method
•    Design-build  method
•    Integrated  project  delivery  method

The design-bid-build method is the oldest and most familiar method of project delivery. This method is covered first. Because the essential features of construction and postconstruction phases are almost identical in all delivery methods, a discussion of what is included in these two phases is presented next. Subsequently, other methods are discussed in terms of how they differ from the design-bid-build method. The table “Project Delivery Methods at a Glance” provides a synopsis of these methods.

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The preconstruction phase generally begins after the construction drawings and specifications have been completed and culminates in the selection of the construction team. The construction of even a small building involves so many specialized skills and trades that the work cannot normally be undertaken by a single construction firm. Instead, the work is generally done by a team consisting of the   general contractor  and a number of specialty subcontractors .

Thus, a project may have roofing; window and curtain wall; plumbing; and heating, ventilation, and air-conditioning (HVAC) subcontractors, among others, in addition to the general contractor. The general contractor’s own work may be limited to certain components of the building (such as the structural components—load-bearing walls, reinforced concrete beams and columns, roof and floor slabs, etc.), with all the remaining work subcontracted.

In contemporary projects, however, the trend is toward the general contractors not performing any actual construction work but subcontracting the work entirely to various sub-contractors. Because the subcontractors are contracted by the general contractor, only the general contractor is responsible and liable to the owner.

In some cases, a subcontractor will, in turn, subcontract a portion of his or her work  to another subcontractor, referred to as a   second-tier subcontractor, Figure 1.6. In  that  case, the general contractor deals only with the subcontractor, not the second-tier subcontractor.

Whether the general contractor performs part of the construction work or subcontracts  the entire work, the key function of the general contractor is the overall management of  construction. This includes coordinating the work of all subcontractors, ensuring that the  work done by them is completed in accordance with the contract documents, and ensuring  the safety of all workers on the site. A general contractor with a good record of site safety  not only demonstrates respect for the workers but also improves the profit margin by lowering the cost of construction insurance.

FIGURE 1.6  Members of the construction team and their interrelationships with each other and the owner. A solid line in this illustration indicates a contractual relationship between parties. A dashed line indicates a communication link, not a contract. The relationships shown here are not absolute and may change with the nature of the project.